Misconception re: frame lines, DOF, compression

[jaapv]

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On 6/9/2023 at 2:48 AM, dpitt said:

If you start cropping an image taken by a 28mm lens at F1.7, you will keep the same DOF distance no matter how much you crop at the same distance. So if you shoot a subject and you have 20cm DOF, you will keep that no matter how the crop is.

But because you are only using part of the available light (you crop the rest away) it is as if you are closing the aperture as you crop further and further. So your 'virtual' lens gets slower and slower:

28 at F1.7
cropped to 35mm gives F2.0
cropped to 50mm gives F2.8
cropped to 70mm gives F4.0

So with the Q you can simulate an M with a 50mm Elmarit, but 50 Summicron and 50 Summilux or Noctilux will have much shallower DOF at the same distance when you use them wide open.

No. Your shutter speed and aperture remain the same. This DOF change has nothing to do with the amount of light which remains exactly the same per square mm. It has to do with magnification. in this context “ light gathering” is bollocks. 

[nicci78]

What is more correct is to think of the Q as a full frame Summilux-Q 28mm f/1.7
At each crop factor it is just like mounting this lens on smaller and smaller sensor. 
At 28mm you retain the full frame of 24x36. 
At 35mm you end up with an APS-H sensor with 1.25x crop factor. 
At 50mm it is an in between APS-C and 4/3 sensors with 1.78x crop. 
At 75mm you are mounting it on a 1 inch sensor just like a Nikon 1 with 2.68x crop. 
At 90mm it is a 2/3“ sensor just like yesteryear premium compacts with 3.2x crop factor. 

So nothing to rave about a 75mm or 90mm equivalent crop on tiny sensors. If you need such magnification, just buy a proper interchangeable lens camera  

 

 

[01af]

vor einer Stunde schrieb Qwertynm:

vor 3 Stunden schrieb 01af:

Decrease effective format size (while keeping the other three parameters constant), and DOF will also decrease.

That’s where you’re wrong.

No, I am not wrong. Instead, it's you who refuses to see the whole picture.

.

vor einer Stunde schrieb Qwertynm:

Look at the two images on page 1 of this thread. 50 mm at f/3.2 vs Q3 at 50 mm f/1.7. DoF is the same.

As a matter of fact, it's 50 mm on 24 × 36 mm format at f/3.2 versus 28 mm on 13.4 × 20.2 mm format at f/1.7. So you changed three out of four parameters.

I was talking about the effect of changing a single parameter.

.

vor einer Stunde schrieb Qwertynm:

Decreasing sensor size increases DoF at the same FoV. Or did your ever hear somebody say I need to shoot micro-4/3 to get a shallower DoF?

That's right. But again: Here, you are looking at the effect of changing two parameters, format and focal length. Fourthirds has more depth-of-field than 35-mm-format—but that is not due to the smaller format. Instead, it's due to the shorter focal lengths required to get the same field-of-view. And the effect of focal length on DOF is stronger than the effect of format size. In fact, DOF is proportional to linear format size (smaller format = less DOF) and at the same time inversely proportional to the square of the focal length (shorter focal length = much more DOF). So at the same field-of-view, the smaller format has more DOF. But at the same focal length (for example, 28 mm in a Leica Q camera), the smaller format has less DOF.

[Qwertynm]

No one is arguing against what you proclaim @01af  i just think you miss the point of the conversation with your interjection. 
 

the broader topic is using the Q3 in crop modes and what equivalent f stops (in terms of DoF) result out of cropping instead if having the actual FL. 
 

sometimes such nuances get lost in online conversations. I think we are all arguing the same point here

[01af]

vor 13 Minuten schrieb Qwertynm:

 I just think you miss the point of the conversation with your interjection.

My interjection was triggered by line #1 in post #1 at the beginning of this thread.

[hoppyman]

I am curious about what size a 50mm lens would be on a hypothetical Q4 (Q50????) I mean the physical volume of such a thing, whether the body dimensions would need to change too and whether the extant sensor would need to change as well.
I used the 35 focal length a lot on the M system and it's superb on SL2. That package is just too large and heavy for ME as an EDC and travel camera.
I would like to update my everyday and travel camera and the CL obviously won't be developed further.
My heresy is that I am convinced of the utility of the Q3 and I have one on order.
 

[cboy]

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Ahmm ..we have calculators now. Lol. I don't see what's the fuss is all about

 https://www.dofmaster.com/dofjs.html

[CCM22]

Hi all, im considering a Q as a do-it-all- (that is relevant for me)-kind of camera. But that make me dependent on the 50mm crop to make portraits. The way I think the 50mm crop would give a depth of field similar to a 50mm f5.6 (too limiting), but consensus in this thread suggest f3.2 (I can work with that!)?

It gives me hope that I’m wrong but I’m struggling to see why it should not be equivalent to a 50mm lens on a ff sensor shot at f5.6 (in terms of dof). Any help to sort this out is appreciated!

 

my thinking is:

a 28mm f1.7 on a full frame sensor shot at 2meters distance have depth of field of 0.52m according to https://www.dofmaster.com/dofjs.html

 

The same site say that a 50mm lens on full frame sensor at 2m have a depth of field of 0.54m at f5.6. (F3.2 have a considerable shallower dof of 0.3m).

In the thread it’s stated that a crop is the same as shooting with a smaller sensor but is that really true? Isn’t the entire full frame sensor used for every photo and if using the crop mode all that is happening is that some meta data tag is added to tell the photo editing software to use a default crop ? Ie it’s practically the same to crop using the in camera crop mode or to do it yourself afterwards in post. In that case the dof should be 0.52m for my example regardless of crop.  Details shouldn’t become sharp/blurry as I zoom/crop into a picture in post?

/C

 

 

[jaapv]

Don’t agonize over DOF. To begin with it is a complete illusion created by the lack of resolution of our eyesight. A photo is only sharp in the picture plane of focus.DOF is the zone of acceptable unsharpness around that plane of focus. Enlarge and itwill reduce. It will be 0 at 100% magnification. Walk away from a print and it will grow.  
There are other ways of subject separation. Colour contrast, normal contrast, perspective, take one step closer, if DOF is your sole tool it will become a cliche. just take your images as you see them and all the theoretical pundits will vanish in a cloud of green smoke. 
 

[Qwertynm]

@CCM22

you‘re going at it wrong. The Q does not have a 50mm lens but a 27mm (after lens corrections). It crops into the image to create the FoV of a 50mm but now with a sensor area that is 1.852x smaller than „fullframe“. So just calculate 1.7 * 1.852 and you‘ll get almost f/3.2. 

 

I believe I posted images in this thread on page one showing the difference of Q cropped to 50 and a real 50 on FF. The real 50 is shot at f/3.2 and the Q at f/1.7. 

[MindsEye]

On 7/14/2023 at 8:41 AM, Qwertynm said:

@CCM22

you‘re going at it wrong. The Q does not have a 50mm lens but a 27mm (after lens corrections). It crops into the image to create the FoV of a 50mm but now with a sensor area that is 1.852x smaller than „fullframe“. So just calculate 1.7 * 1.852 and you‘ll get almost f/3.2. 

 

I believe I posted images in this thread on page one showing the difference of Q cropped to 50 and a real 50 on FF. The real 50 is shot at f/3.2 and the Q at f/1.7. 

Yes, you're right and @jaapv also makes a great point about the relativity of depth of field when you consider all the factors such as viewing distance, circle of confusion, an individual's eyesight, etc.

When I started this discussion it was simply to point out that some reviewers didn't understand the relationship of DOF and aperture. And also that, for me anyway, the Q3 is also useful for 35mm and 50mm equivalents (yes cropped, not actual lenses.) Because of the large sensor, there is useable resolution when cropping, even for large prints. Among other aspects of my full time photography business, I sell large prints to my patrons. So that is my perspective. Others on the forum have their own needs and desires.

So far I love my Q3 and I find the 35mm and 50mm crops useful. Sure they are only framelines for cropping but framelines are something I can relate to, going back to my early days of photography in the 70s, using a 1940s vintage rangefinder and my first use of Leica rangefinders in the early 80s. I would still like to see a visual zoom option on the Q3 as I have on my X-T5 bodies but I can live with the framelines.

I have other cameras and fast primes if I need them but it's hard to beat the Q3 for a take-it-with-you-everywhere camera. The lens and sensor are both stellar and I find myself saying "wow" a lot when I am culling and editing. I find the Q3 images need less tweaking than my Sony FF images. Fujifilm of course has fabulous film simulations so also not as much processing required but still not quite the same sense of wonder looking at those versus the Leica.

As I often tell my workshop attendees, the whole point of photography is enjoyment. So pick up whatever camera brings you joy using it and go enjoy yourself.

Edited July 17, 2023 by MindsEye

[CCM22]

Thanks @jaapv , @Qwertynm  and @MindsEye for helping me out.
 

Especially @jaapv comment on dof being a subjective concept of acceptable sharpness got me thinking. If I increase the size of the crop to the original non-cropped size dof will become shallower. I think this was the missing step in my reasoning.

And i agree that spending to much time on these technical aspects is of limited use if one wants to be a better photographer, BUT I would argue that ”photography gear” is a perfectly  enyoyable interest on its own to spend your time on! 😀

I think of it as having an interest in, let’s say, fighter jets and enjoying reading up on every detail without even having the slightest possibility or even wanting to actually fly one!

/C

[Qwertynm]

vor 6 Stunden schrieb CCM22:

”photography gear” is a perfectly  enyoyable interest

Totally! That’s why most people are on this forum. Enjoy

[RTP]

Howdy Y'all,

My take and dive into Leica coming from Lumix is wanting a one lens RF camera for impromptu carry.

Ya know, keep it simple and stealth.

Having the S1R out of others and the 47.5mp resolution is quite liberating with a fast prime or zoom; however itsa beast at times and target in others.

RF bodies for me is less intimidating for a quick portrait of a brief encounter with a compliant subject.

I often read that fashion photographers shoot a 50mm at f4 and 8. I might go f4 and mostly much wider a controlled environment.

When I thought about it, I realize my immediate trigger pull was the Q3 feature set. Subconsciously all of them was all it took and now as I get nervous upon it's arrival...the truth of the matter and why I bore you is that the nature of the Q is the satisfactory execution and features that exude the decisive moment...for me...and so, I think I'm Ok with that lens and crop-mode. My shots will be in focus and my subject will have hoped into an taxi...bye bye..

My kool kit for serious shoots is at the ready as always. I've studied the image results from the series of the Q's and there is a uniqueness that has it's place in my quiver or so I tell myself as I wait for that knock on the door.

Tim

[kiwidad]

On 6/8/2023 at 7:48 PM, dpitt said:

If you start cropping an image taken by a 28mm lens at F1.7, you will keep the same DOF distance no matter how much you crop at the same distance. So if you shoot a subject and you have 20cm DOF, you will keep that no matter how the crop is.

But because you are only using part of the available light (you crop the rest away) it is as if you are closing the aperture as you crop further and further. So your 'virtual' lens gets slower and slower:

28 at F1.7
cropped to 35mm gives F2.0
cropped to 50mm gives F2.8
cropped to 70mm gives F4.0

So with the Q you can simulate an M with a 50mm Elmarit, but 50 Summicron and 50 Summilux or Noctilux will have much shallower DOF at the same distance when you use them wide open.

So according to your logic if I take a picture at 28 and print it out and cut 50mm crop out it will have a different exposure? The camera just crops the sensor doesn't it so why would exposure change? If you actually change the true focal length then I think you are correct but that isnt happening here!

[Daniel C.1975]

As an engineer I still don't get the ongoing discussion since, I believe the first DSLR (which had a 1.5 crop sensor), around DOF, focal length etc. pp. In the end it is very simple physics and no rocket science. 

Still, for around 20 years you hear the same arguments over and over again, which are from a technical aspect most of the time just nonsense (e.g. "A 50mm crop from a 28mm lens will still have the perspective distortion of a 28mm lens", or "the compression will be different" ...  --> busted bollocks). 

To put it simple: There are advantages and disadvantages, but bending physics is not playing a role in it

 

I for sure don't want to offend anyone who just want to understand what the impacts and implications are - questions, discussions and gaining knowledge are of course an essential part of a forum. In fact, I don't want to offend anyone.   - 

 

 

Edited July 28, 2023 by Daniel C.1975

[Qwertynm]

This thread keeps on giving. Let it rest already 😅

 

@kiwidad: look at the responses after your quoted post. 

[kiwidad]

On 7/28/2023 at 6:42 AM, Qwertynm said:

This thread keeps on giving. Let it rest already 😅

 

@kiwidad: look at the responses after your quoted post. 

I did! its an interesting discussion of apples and oranges. 

I'll leave it this thought... If  I enlarge a print do I reduce perceived depth of filed?

[city of bristol]

What people forget to mention when they talk of depth of field ,eyesight, focus stacking etc is the human brain  which is not at all interested in all that stuff. 

People and especially the 99% non photographers just look at an image and sometimes feel a positive emotional response to it , the brain takes short cuts when it analyses such things even with massive prints!

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Hallo,

Look here: Leica Q

[Qwertynm]

vor 3 Stunden schrieb kiwidad:

If  I enlarge a print do I reduce perceived depth of filed?

I‘d say up to a point or it depends. If you‘ve ever digitized 135mm film those tiny 24x36mm images don’t have great depth. Once you view them on the monitor (or on paper), you have a better perception of depth. So the perceived depth of field is reduced, yes (imho).
 

But you can’t leave out viewing distance. If you’re far enough away, everything will look in focus. Same with smaller prints. They will look less blurry than bigger ones. But I thibk this is more related to viewing distance. 
 

but that’s not what this thread was about either if I remember correctly 🤔

Edited July 29, 2023 by Qwertynm